Railway traffic controlling apparatus



y 2, 1942- H. s. Y ouNG 2,282,841

' RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Aug. 2'7, 1941 2 Sheets-Sheet 2 BZHGPH HIS ATTORN EY Patented May 12, 1 9 42 when i UNITED STATES PATENT OFFICE ABPARATUS Henry S. Young, Wilkinsburg, Pa.,'assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application August 27, 1941, Serial' No. 408,483

e'oiaims. (011246-26) My invention relates to railway trailic controlling apparatus 'and it has particular reference to the organization of such apparatus into novel and improved systems for controlling railway traffic from a remote control point. More particularly, my invention relates to remote control or centralized trai'lic control systems of the type wherein three-position control of the rear signal of two independently controllable signals governing trafiic movements in the same direction over a stretch of track is governed by the advance signal in accordance with the polarity of current applied to a two-wire line circuit extending between such signals, and in which traffie locking for preventing conflicting traffic movements over the stretch is attainedover the same two-wire line circuit.

An object of my invention is the provisionfln a system of the above described class, of novel and improved meansgoverned by the advance signal for controlling the. polarity of current applied to a two-wire line circuit, whereby to effect control of the rear signal of a pair of successive signals governing tIELfiC over a stretch of track. I

Another object is the provision, in a system of the class described, of means whereby control established by an advance signal over'the polarity of current supplied to a two-wire line circuit is made dependent upon the rear signal being conditioned for control over such'line circuit.

A further object is the provision, in a signal system wherein signals governing trafiic in opposite directions are controlled over circuits employing but two line wires, and inwhich the relative polarity of current applied to a line circuit at one end or the other may be reversed to provide three-position control of the signals for both directions, of novel and improved means for preventing reversal of current polarity at one end or the other of a line circuit in such manner as to connect two current sources to the line circuit in additive relation.

An additional object is the provision of novel and improved means for controlling therelative polarity of current supplied to the two-wire line circuit 'of a signal system of the class disclosed in United States Letters Patent No. 1,650,575, granted on November 22, 1927, to 'Herbert A. Wallace.

The above-mentioned and other important ob jects and characteristic features of my invention which will become readily apparent from the following description, are attained in accord- 'ance with my invention byproviding a system of the class describedand'having a two-wire line circuit provided with a source of current adjacent theadvancesignal forcontrolling the rear signal in accordance with the polarity of current supplied from the sourceto the circuit, with means governed by the advance signal and'rendered effective to control the polarity of current supplied to the-line circuit when and onlywhen therear signal is} conditioned for control over theline circuit.

I; shall describe several forms of apparatus embodyingmyinvention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a V diagrammatic view illustrating one form of apparatus embodying-my invention. Figs. 2, 3 and 4 are diagrammatic views each showing modifications of a portion of the apparatus shown in Fig-. l. I I u In each of the several views; similar reference characters have been employed to designate corresponding parts.

Referring to the drawings, the line diagram atthe top ofFig. 1 represents a stretch of railway track divided into a plurality of successive adjoining insulated track sections IT, 2T andr3T. Each section" of track is provided in the usual manner with a closed circuit track circuit in cluding a normally energized trackrelay, designated" by the reference character TR with a suitably distinguishing prefiX, and the association ofeach track relay with its section is indicated conventionally by a dotted line extending from the track relay to its: associated section. A siding or passing track is connected to section IT by a switch IS, while another siding or passing track is connected to section 3T by a switch 38. These switches S may be operated, preferably by power, in any suitable manner ,by means not comprising a part of mypresent invention and hence not illustrated in the drawings. a

The movement of eastbound trafiic, operating over the stretch of track from left to right as viewed in the drawings, is governfid by a pair of signals R2 and R4, while westbound traiilc operating over the stretch is governed by a pairof signals L2 and L4. These signals are preferably capable of displaying three aspects, and may be of any suitable type such as searchlight, position light, colorlight, etc. For the purposes of the present description, I shall assume that the signals R and L are searchlighttype signals, each of which is provided with a circuit controller which compri'ssone" or more movable contact members The other contact member 1 is operated by the 1 signal mechanism and engages contact member...v It or I I according as the signal displays its'cle'a'r or either its caution or stop indication.

In order to simplify the drawings and. tofassist in tracing circuits, the circuit controllers associated with signals L2 and R4 have been represented in the drawings at points remote from the location of the associated signals, and the association of a controller with a signal is indicated by placing above the controllerthe reference character'of the associated signal. Also, contacts have been represented in the drawings disposed remote from the relays operating such contacts, but in each of such cases the relay operating the contact has been indicated by placing above such contact the reference character of its associated relay.

Signals R2 and L2, which govern opposing traffic movements through section IT, are controlled from a remote office station through the medium of field station apparatus preferably disposed adjacent section IT and comprisingtwo remote or code controlled stick relays one for each signal and each designated by the reference character HSR with a prefix corresponding to the reference character of its associated sig-' nal. The system for controlling the HSR relays from a remote office station may be a direct wire system using a line wire for each relay, or may be a code system in which all of the relays are controlled over a single circuit; I shall assume that the remote control or centralized trafiic control system employed is of the time code type shown in United States Letters Patent No. 2,229,- 249, granted on January 21, 1941, to L. V. Lewis. In such a system, a line code storage unit, designated by the reference character LCS, is provided for each field station and comprises apparatus selectively operated in response to code signals sent from the central office station. When a storage unit is operated, energy is made to appear at a terminal I 2, l3 or .14, according to the code signal operating the unit. Energy is applied to terminal l2 or l3 of the operated unit only during the reception of the code signal to pick up the selected HSR relay. Energy remains on terminal 14 of the operated unit subsequent to the sending of the code signal to hold the selected HSR relay energized over a stick circuit.

, Signals R4 and L4, which govern opposing trafiic movements over section 3T, are likewise controlled from the remote oflice station through the medium of field station apparatus preferably disposed adjacent section 3T and comprising a line code storage unit LCS and stick relays R4HSR and L4HSR. Relay R4l-ISR or L4HSR is picked up according as positive energy is applied to terminal 12 or 13, respectively, and such relay is held up over its stick circuit made effective when energy is applied to terminal [4.

The signals R2 and L4, which govern opposing traffic movements over section 2T intermediate the two siding tracks, are additionally controlled by apparatus associated with the field station apparatus and incorporating tramc locking means arranged to prevent simultaneous clearing of both signals, thereby preventing conflicting traffic movements through the signaled stretch. These means comprise two trafiic locking relays, one 'for each signal R2 and L4, and each designated by the reference character ZR with a prefix corresponding to the reference character of the associated signal. Each traflic locking relay ZR has a back contact interposed in the pickfup'circuit of the code controlled HSR relay of the associated signal, hence relay RZHSR for example may be picked up by the communication system When and only when relay RZZR is released to close its back contact I5, and relay L4I-ISR may be picked up over the communicationsystem only when relay L4ZR is released.

The traffic locking relays ZR are controlled .by a two-wire line circuit extending from the field station apparatus adjacent section IT to the field station apparatus adjacent section 3T. Each end of such circuit has associated therewith asuitable source of current such as a battery designated by the reference character SB with a suitably distinguishing prefix, and each end of such circuit also has associated therewith pole changing means, hereinafter referred to, for controlling the polarity of current supplied by the adjacent source of current to the line circuit. Each end of the line circuit also has associated therewith switching means, to be referred to hereinafter, for either connecting the two-wire line circuit to the adjacent source of current or conditioning such circuit to effect control of the adjacent one of the two signals R2 and L4.

The switching means may comprise as shown in Fig. 1, slow release repeater. relays one for each signal control relay RZHSR and L4HSR, and which repeater relays are designated by the reference character F with a prefix corresponding to the prefix employed in the reference character of the associated HSR relay, Repeater relay MB is controlled, for example, over a circuit extending from one terminal B of a suitable source of current, such as a battery not shown but having its opposite terminals designated by the reference characters 13 and'C, through front contact l6.of its associated relay L4HSR, the winding of relay ME, and back contact I! of traffic locking relay L4ZR to the other terminal 0 of the source of current. Relay MP has connected across its terminal an obvious shunt circuit'path completed when back contact I6 of relay L4HSR is closed, whereby relay L4F may be made slow to release. The other relay RZF is similarly controlled by relay RZHSR, as is readily apparent from an inspection of the drawmgs.

'- As shown in Fig. 1, the signals R2 and L4 are arranged to be controlled by signal control relays RZHD and L4HD, respectively, which relays are normally disconnected from the twowire line circuit. One signal control relay HD or the other is at times connected to the line circuit, to condition its associated signal for control over such circuit, at such times as the switching or repeating rela F of the associated stick relay HSR associated with signal R2 or L4 is picked up. These relays HD are preferably of the slow pick-up, retained neutral type of polarized relay which incorporates means, such as hold-down pole pieces, arranged to dclaythe pick-up of the neutral armature of the. relay.

The manner in which arelay HD controls its associated signal is not represented in the drawings since such control may take any one of many forms well known in the art. a For the purposes of this description, therefore, it is deemed sufficient to state that whena relay HD. is deenergized, its associated signal is caused to displayits stop indication; when relay HD. is energized by current of one relative or normal polarity, its associated signal is caused todisplay an approach indication; and when a relay HDis energized by current of the other or reverse polarity, the associated signal is caused to display its clear indication.

The pole changing means, hereinbefore re ferred to, comprise relays designated by the reference character PCR with. suitably .distinguishing suffixes, and arranged in a manner to be made clear hereinafter, to become energized only after the adjacent trafficlocking relay ZR is picked up.

The apparatus embodying my invention is in its normal condition, as represented in Fig. 1, when all code controlled relays HSR are released and the signaled stretch of track is unoccupied. In this condition of the apparatus, eastbound signals R2 and RA and westbound signals L2 and L4 display their respective stop aspects; and the track relays TR are allpicked up. The switching relays F and the pole changing relays PCR are deenergized, and the sources of current at the ends of the two-wire line circuit are connected in series opposition over a circuit which may be traced from one terminal of battery ISB, through asymmetrical unit 2! in its'low resistance direction, the winding of relay RZZR, back contact 22 of relay LZPCR, back contact 23 of relay R21 front contacts 24, 2-5 and 26 of relays I'IR, 2TB and 3TB, respectively, back contact 21 of relay LF, back contact 28 of relay RAPCR, the Winding of relay LQZR, asymmetrical unit 29 in its high resistance direction, the one terminal of battery SB, through the battery to the other terminal of battery 2S3, back contact 30 of: relay R'4PCR, back contact 3| of relay LAF, front contacts 32, 33 and 34 of relaysSTR, 2TR and I'I'R, respectively, back contact 35' of relay RZF', back contact 36 of relay LZPCR, and to the other terminal of battery ISB. Relays. R2ZR and L4ZR are deenergized since with the batteries I SB and ZSB connected in opposition, substantially no current flows in the line circuit. Also, the asymmetrical units 2| and 29, interposed in the line circuit, function to prevent a current flow and hence energization of either traffic locking relay ZR should the electromotive forces of the two batteries become unbalanced when. such batteries are connectedinseries opposition.

If, now, the operator wishes to authorize a westbound movement over the stretch, he will under normal conditions, first control the communication system to cause relay L4HSR to-pick up, thus causing repeater relay LAF to become energized over its circuit previously traced and including front contact 16 of relay L4HSR and back contact I? of relay LAZR. The energization of relay LQF causes its back contacts 21 and 3| to open to disconnect relay LQZR and battery ZSB from. the line circuit, and front contacts 21 and i of relay LQF close to connect relay L4HD to the line circuit and thus condition signal L4 for control over suchcircuit, which circuit now includes front contact 38 of relay MHSR' andthe winding of relay: LAH-D. I shall assume that-the current supplied from battery I SB to theli'ne circuitfwhen pole changing relay: LZPCR-is released, i's of" the one relative polarity: and causes relay- LAHD to be energizedin. the direction to cause its-associated signaliL todisplayits-approach indication. Relay RZZR is at this time energizedand opens itsback contact [-5, thereby-opening the pick-up circuit of relay R-Zl-ISRtoprevent energization of such relay over the communication system. It follows, therefore, that: with relay L4HSR. energized to control signal-L4- topermit a westbound movement, the opposing signal R2 cannotbe controlled by the operator over the communication system, and hence conflicting traffic movements are prevented.

After having'established'control:over westbound signal LG, the operator will then clear westbound signal L2 by suitably controlling the communication system to pick up relay LZI-ISR, whereupon signal L2 iscaused' to: display either its caution or its proceed indication in accordance with traffic conditions in advance;

LZPCRassociated withfi'signal L2 accordingly-'be- Pole changing relay ll of relay R2ZR, hence it follows that pole changing relay. LZPCR may be picked up only if trafliclocking relay RZZRcis picked up; Also, it

is. to. be noted that a resistor. 4011s. connected across the terminals. of relay LZPCR. when front contact ll" of relay R-ZZR. is closed. The-function of resistor 40.- willibe pointed out. hereinafter.

The energizationof relay LZPCR causes its frontcontactsZ-Z and 3.6. to close and pole; change the current supplied from. battery l-SB tothetwowire line circuit, thereby-causing: the current supplied to. relay. LAHD to have a polarity. such, as to cause the relay to swing. its polar contact members'to their other positions to cause 'si'gnal'L l to. display its clear. indication. The. rearisi'gnal L4v is, therefore, controlled: bythe advance signal in accordance with the. polarity of; current. sups plied over the two-wire line circuit;

At this time, itLShOllldbe noted that the. apparatus embodying my invention. is 50: arranged as to prevent a. 10cked-up' condition; if the op.-

erator authorizes a westbound movement by firstclearing signal L2. For; example, if the apparatus of Fig. l. is inits normal condition as repclosed and batteries ISB and 28B are not con- ,7

nected' in additive relation, as would happen if the pole changing means of the circuit were operated by and directly repeated the position of signal L2. It follows, therefore, that the arrangement is'such-as'to avoid improper energization of both advance trafiic locking relays RZZR; and L4ZR, caused by the; additive relation of both batteries of the-two-wire line circuit, when the advance signal L2 is cleared prior to clearing rear'signal L4.

Under the conditions assumed; that is, with signal L2 cleared, the operator may clear signal L4 by causing the communication system to pick up relay L4HSR, thereby causing switching relay L4F to pick up and connect control relay L4HD to the line circuit to condition signal L4 for control over such circuit. When this happens, relay R2ZR of course picks up since battery ISB is no longer opposed by battery 2SB, and front contact ll of relay RZZR closes to complete the circuit of pole changing relay LZPCR, whereupon that relay picks up to close its front contacts 22 and 36 to cause the current supplied from battery ISB to the line circuit to have the polarity such as to cause relay L4I-ID to swing its polar contact members to their positions wherein signal L4 is caused to display its proceed indication. The slow pick-up characteristics of the retained neutral polarized relay L4HD are selected to be such that relay L4HD does not pick up its neutral armature until after relay LZPCR picks up to pole change the current supplied to the line cir-. cuit, thereby to avoid a transitory display of the caution indication of signal L4, such as would occur if relay L4HD immediately picked up when first connected to the line circuit when relay LZPCR is released to cause current of the one polarity to be supplied to the line circuit. It follows, therefore, that under the conditions assumed, signal L4 will be caused to operate from its stop directly to its clear position and a transitory display of the caution indication is prevented.

Signal L4 is, of course, caused to display its stop aspect when the train enters the stretch and shunts any one or more of the track relays ITR, 2TB or 3TR to cause the two-wire line circuit to become opened. After the westbound train vacates the stretch, signal L4 is first caused to display its caution indication, due to signal L2 being controlled to its stop position in accordance with the usual practice by apparatus not shown in the drawings, and then after signal L2 is caused to display either its caution or its clear indication, signal L4 i caused to display its clear indication.

The signals may be manually set to stop by the operator suitably controlling the communication system to cause the release of relays L2HSR and L4HSR. Ordinarily, the operator will first set signal L2 to stop, whereupon the circuit controller operated by signal L2 assumes its normal position to deenergize pole changing relay LZPCR, which relay at this time has resistor 40 connected in multiple with its winding,'hence the relay is made slightly slow to'release. .At the end of its slow release interval, relay L2PCR releases to close its back contacts 22 and 36 to cause battery ISB to apply current of normal polarity to the two-wire line circuit.

Signal L4 ordinarily is controlled by the operator to its stop position immediately after signal L2 is set to stop, and the slow release interval of relay LZPCR is preferably selected so as to main tain such relay picked up until relay L4I-ISR is released over the communication system; thus causing front contact 38 of relay L4HSR interposed in the two-wire line circuit, to open and thus open that circuit and cause the release of relay L4HD. Front contact l6 ofrelayL4HSR also opens to open the circuit of switching relay L4F. Relay LZPCR is adjustedto release prior to the release of relay L4F which latter relay is made slow to release, in part due to the shunt circuit path connected across its terminals through back contact l6 of-relay L,4 I-ISR, h ence it follows. that when signals L2 and L4 are sequentially set to stop by the operator, the rear signal is caused to operate directly from its clear position to its stop position without causing a transitory display of its caution indication; and that when switching relay L4F releases, the batteries ISB and 2SB are connected in their normal opposed relation.

In the event that signal L4 is manually put to stop prior to signal L2 being put to stop, by the operator suitably controlling the communication system to release relay L4HSR, front contact 38 of relay L4HSR opens to open the twowire line circuit, thereby deenergizing relays L4HD and RZZR. Relay RZZR thereupon releases, and opens its front contact 11 to deenergize pole changing relay LZPCR, which relay releases immediately, since with front contact I! of relay R2ZR open, resistor 40 is not connected across relay L2PCR to delay its release, and back contacts 22 and 36 of relay LZPCR. close to cause battery ISB to supply current of normal polarity to the line circuit. Slow release relay L4F, which becomes deenergized when front contact l6 of relay L4HSR opens, is proportioned to remain picked up until after relay L2PCR releases, hence when relay L4F releases, the two-wire line circuit is restored to its normal condition as represented in the drawings, and in which condition batteries ISB and 2SB are connected in series opposition. Signal L2 may, of course, be set to stop when the operator causes the communication system to release relay LZHSR.

With the apparatus in its normal condition, as shown in the drawings, the operator may authorize an eastbound movement by suitably controlling the communication system to cause relays RZHSR and R4HSR to pick up. The apparatus operates in such event to clear signals R2 and R4, in a manner believed to be obvious from an inspection of the drawings taken in connection with the foregoing detailed description of the operation of the apparatus for clearing the westbound signals L2 and L4, and further detailed explanation is deemed unnecessary.

Figs. 2, 3 and 4, each show modifications of the signal control portion of the two-wire line circuit represented in Fig, 1. In Fig, 2, operating windings 50 of the signal mechanisms are illustrated as being energized directly from the twowire line circuit, and the slow pick-up. retained neutral polarized relays HE, employed in Fig. 1, are dispensed with. The apparatus, modified as shown in Fig. 2, operates in a manner believed to be obvious from an inspection of the drawing, it being noted however, that the apparatus of Fig. 2 might cause the rear signal, such as signal L4, to display a transitory caution indication if signal L2 is cleared prior to signal L4. This transitory caution indication results from the fact that pole changing relay LZPCR. is picked up only after signal L4 is conditioned for control over the line circuit, hence after signal L4 is connected by relay L4F to the line circuit, current of normal polarity is first supplied to the line circuit over back contacts 22 and 36 of relay L2PCR during the pick-up interval of relays R2ZR and L2PCR. This current of normal polarity might cause signal L4 to display its caution indication. Then, after relay LZPCR picks up, current of the other polarity is supplied to the line circuit and will cause signal L4 to display its clear aspect.

In Fig. 3, the slow release repeater relays RZF and L4F, employed in Figs. 1 and 2, are dispensed with. The switching means for the two-wire line circuit now comprise contacts operated by the 'front contacts 53 and 54 of relay LAHSR close remote or code controlled relays I-ISR associated with the rear signals R2 and L4, and each of these code controlled relays is--provided with a slow pick'up repeater 'relay, designated by the reference'character GR with a prefix corresp nding to the prefix employed in the reference character of the associated code controlled .HSR-relay. Each repeater relay GR controls the energization of the operating winding 50 of the associated signal operating mechanism by connecting such winding to or disconnecting it from the two-wire line circuit. For example, relay LAGR is -normally 'deenergized and its back contact :52 is closed to -condition thetwowire line circuitin-t itially to be completed through a resistor 5| when front contacts 53 and 54 of relay LGHSR. close. At the end of' its slow pick-up interval, relay L lGR picks up to open its back and close its front contact 52, thereby connecting operating to connect windingill in circuit with the two-wire line circuit, the shunt path across winding 50 is opened only at the end of the interval required for relay LTER to open its thermal contact 58.

This interval is selected to bridge the pick-up winding 56 to the two-wire lir-re circuit. The

slow pick-up characteristics of the repeater relays GR are selected to bridge the pick-unintervals of the tra-fiic locking relays ZR and pole,

changing relays PCR, thereby to prevent a transi tory display of the caution indication by the rear signal ifthe advance signal is first to clear. When an advance signal is cleared, as when signal L2 :is cleared, and the rear signal L4 is subsequently controlled by the operator to its clear,

condition, relay 'RJZR. is picked up whencode controlledrelay L4HSR picks up, and relay LtPCRaccord-ingly picks'up to reversethe polarity of energy supplied tothe line circuit prior to repeater relay LGGR picking up to connect the line circuit 'to operating winding 5c of the mechanism of :signal L4. It follows, therefore, that when relay LGR picks up, the current polarity in the line circuit is "such as to cause signal L4 to operate directly to its-clear gposition. L

In Fig. 4, thermal time element relays TER, and signal repeater relays RGPR are provided and are arranged to prevent :a transitory display of the cautionindication when arradvance signal is cleared prior toitsassociated rear signal being cleared. Each rear signal R2 and L4 controls its associated repeater relay RGBR- over .an obvious circuit shown in Fig. =4 and completed when the signal is in its stop position. Each-time element relay 'I'ER is providedwith an energizing circuit controlled by the adjacent repeater :relay RGPR and the code controlled relay associated with the associated signal. For example, relay LATER is provided with a circuitextending'from terminal B through front contact56- of relay LAI-ISR, front contact .5 of *relay L lRGP-Rand the thermal unit of relay LdTER to terminal 0.

The repeater relays RGPR and time element relays TER of Fig. 4 cooperatein' controlling. a shunt path connected'across operating winding 59 of the associated rear signal R2 -0r L4,, and thereby delays the energization of-such operating winding in a manner substantially corresponding to the manner that repeater relays G-Rin Fig. -3 delay the energization of the operating windings 50 of the signal mechanisms of Fig. 3. Forexample, in Fig. 4, repeater relay L4RGPR is normally energized while thermal relay LAT-ER is 'deenergized. Acircuit path, connected throughfront contact 59 of relay L lRGPR and normally closed thermalcontact 58 of the thermal relay L4TER, is therefore-connected in multiple with operating winding 55 of the signal mechanism of signal L4. It follows that when signal control relay LAI-ISR is picked up after relay LZHSR is picked up, and

intervals of relays RZZR. and L2PCR, shown in supplied to such winding is of the properpolarity to cause the signal to operate directly to its clear position. When this happens, repeater relay LARGPR releases to open its front contact 51, thereby opening the energizing circuit of thermal relay L lTER. Frontcontact 59 of relay LQRGPR also opens so that when thermal contacttii of relay LQ'IER again closes, the shunt path around winding 5!] 'of signal L4 is maintained open.

. Although I have herein shown and described only a .few forms of railway trafiic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the. scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described claimis: V 1 v 1; In combination, a stretch of railway track, two successive signals governing traific in the same direction through said stretch, a twoewire line circuit having a source of current adjacent the advance signal forcontrolli-ng the rear signal I in accordance with the polarity of current applied by said source to said line circuit; independently operable control means for each signal, means governed by the control meansvas sociated withsaid rear signal for conditioning said signal ,for control over said line circuit, meansgoverned by the control means associated with said advance signal for controllingthe po-' larity of current applied from said source to said line circuit, and means associated with said line circuit adjacent said advancesignal for rendering ineiiectivesaid last-mentioned means unless said rear signal is conditioned 'for control over said line circuit.

2. In combination, a stretch of railway track, two successive signals governing traffic in the same direction through said stretch, a two-wire sociatedwith said'rear signal for. conditioning said rear signal for control over said line circuit, a source of current, means governed by said advance signal for controlling the polarity of cur-- rent supplied from said source to-said circuit, and

means associated with said line "circuit at said advance signal for preventing control by said advance signal of said current polarity until said rear signal is conditioned for control over said line circuit;

3. in a railway signalysyste'm fora stretch .of railway'track provided with two successive signals Jgoverning trafiic in the same direction through the stretch,'sa'id signal system comprising independently operable control means for each signal, -a two-wireline circuit having a source of current adjacent the advance signal for controlling the rearsignal in accordancewith the polarity of current applied by said source to the my invention, what I s line circuit, and means governed by the control means of the rear signal for conditioning said rear signal for control over said line circuit, the combination in such a signal system of means interposed in said line circuit adjacent said source and operative when said rear signal is conditioned for control over said line circuit, and means governed by the control means of said advance signal for controlling the polarity of current applied by said source to said line circuit when and only when said last-mentioned means is operative.

4. In combination, a stretch of railway track provided with a pair of successive signals governing traflic in one direction and another pair of successive signals governing trafiic in the opposite direction through said stretch, independently operable control means for controlling each of said signals, a line circuit for controlling the rear signal of each of said pairs in accordance with the polarity of current applied to said circuit, two sources of current one at each end of said line'circuit and two locking relays one associated with each source, means governed by the control means associated with each of said rear signals for at" times conditioning such signal for control over said line circuit and at other times for connecting the adjacent source and locking relay to said line circuit, whereby to energize a locking relay by current from its associated source only when the rear signal at the opposite end of the line circuit is conditioned for control over said circuit, and means governed by the advance signal of each pair for controlling the polarity of current supplied to said circuit whenthe locking relay at the adjacent end of the line circuit is energized.

5. A. railway signal system, provided for a stretch of railway track having an advance and a rear signal for governing traflic in the same direction through said stretch; said signal system comprising independently operable control means for each signal, two sources of current one for sources in a series circuit with said sources connected in opposing relation, whereby said two locking relays are normally released, means governed by the control means of each rear signal for at times disconnecting the adjacent source and locking relay from said circuit and for conditioning such rear signal for control over said circuit, whereby to energize a locking relay by current from its associated source only when the rear signal at the opposite end of said circuit is conditioned for control over said circuit, and pole changing means governed by the advance signal of each pair for at times controlling the polarity of current supplied to said circuit from its adjacent source; said system being characterized by the fact that the pole changing means associated with each advance signal comprises a relay energized over a circuit including inseries a contact of the associated advance signal closed only when said signal is cleared and a front contact of the locking relay associated with such signal.

7. A railway signal system. provided for a stretch of railway track having a pair of successive signals governing traflic in one direction and another pair of successive signals governing traffic in the opposite direction through said stretch, said signal system comprising; independently operable control means for controlling each of said signals, two sources of current and two locking relays, one of each for the advance signal of each pair of signals, two slow pick-up retained neutral polarized control relays one for each of the rear signals, a line circuit for normally connecting said two locking relays and said two sources in a series circuit with said sources connected in opposing relation, whereby each signal and a locking relay for the advance signal, a line circuit for normally connecting saidlocking relay and two sources in a series circuit withsaid sources connected in opposition, whereby said locking relay is normally released, means governed by the control means of said rear signal for at times disconnecting the associated source from said line circuit and for conditioning said rear signal for control over said line circuit in accordance with the polarity of current supplied from the other source through said locking relay to said line circuit, and pole changing means associated with the advance signal and controlling the polarity of current supplied from the said other source to the said line circuit to cause said current to have one relative polarity or the other; said system being characterized by the fact that said pole changing means comprises a relay energized over a circuit including a front contactoi said locking relay and a contact closed only when said advance signal is cleared. 5

6. A railway signal system provided for a stretch of railway track having a pair ofsuccessive signals governing traffic in one direction and another pair of signals governing traflic in the opposite direction through said stretch, Said signal system comprising; independently operable control means for controlling each of said signals, two sources of current and two locking relays, one of each for the advance signal of each pair of signals, a line circuit for normally connecting said two locking relays and said two said two locking relays are normally released, means governed by the control means of each rear signal for at times disconnecting the adjacent source and locking relay from said circuit and for connecting to such circuit the control relay of such rear signal, whereby to energize a locking relay by current from its associated source only when the control relay of the rear signal at the opposite end of said circuit is connected to said circuit, and pole changing means governed by the advance signal of each pair for at times controlling the polarity of current supplied to said circuit from its adjacent source; said system being characterized by the fact that the pole changing means associated with each advance signal comprises a relay energized over a circuit including in series a contact of the associated advance signal closed only when said signal is cleared and a front contact of the looking relay associated with such signal.

8. A railway signal system provided for a stretch of railway track having a pair of successive signals governing traffic in one direction and another pair of successive signals governing traflic in the opposite direction through said stretch, said signal system comprising; independently operable control means for controlling each of said signals, two sources of current and two locking relays, one of each for the advance signal of each pair of signals, a line circuit for normally connecting said two locking relays and said two sources in a series circuit with said sources connected in opposing relation, whereby said two locking relays are normally released,

means governed by the control means of each rear signal for at times disconnecting the adjacent source and locking relay from said circuit and for connecting to such circuit the operating element of such rear signal, whereby to energize a locking relay by current from its associated source only when the operating element of the rear signal at the opposite end of said circuit is connected to said circuit, and pole changing 'means governed by the advance signal of each pair for at times controlling the polarity of current supplied to said circuit from its adjacent source; said system being characterized by the fact that the pole changing means associated with each advance signal comprises a relay energized over a circuit including in series a contact of the associated advance signal closed only when said signal is cleared and a front contact of the locking relay associated with such signal,

and being further characterized by the provision of means effective when a rear signal operating mechanism is connected to the line circuit, to-

initially shunt such mechanism for a predetermined time interval.

9. The signal system of claim 8 characterized by the fact that two time element relays, one for 

